removeElement.java

/*
	Remove Element

	Given an array and a value, remove all instances of that value in place and return the new length.
	The order of elements can be changed. It doesn't matter what you leave beyond the new length.

*/

// overwrite the target elem
public class Solution {
    public int removeElement(int[] A, int elem) {
        if(A==null || A.length==0) return 0;
        int l=A.length;
        int index=0;
        for(int i=0; i<l; i++){
            if(A[i] !=elem){
                A[index++]=A[i];
            }
        }
        return index;
    }
}

// swap target elem to the end of the array
public class Solution {
    public int removeElement(int[] A, int elem) {
        if (A==null || A.length==0) return 0;
        int i=0, j=A.length-1;
        while (i <= j){
            if (A[i] == elem)   swap(A, i, j--);
            else i++;
        }
        return j+1;
    }
    
    public void swap(int[] A, int i, int j){
        int tmp = A[i];
        A[i] = A[j];
        A[j] = tmp;
    }
}